Titanium Suicide Research Articles

Silicide Identification in Rta-Processed Ti Salicide by Analytical Electron Microscopy

Titanium suicides have low resistivity, low contact resistance, and are widely used as interconnects in electronic devices. The most desirable structure is the C54 variant of titanium disilicide (TiSi2). It is typically formed during thermal annealing by a polymorphic transformation from the C49 TiSi2 structure. The C49 to C54 transformation has been studied extensively and there has been substantial effort to devise ways in which to lower the temperature associated with this transformation. This research uses high-resolution imaging (HREM), convergent-beam diffraction (CBED), and energy-dispersive X-ray microanalysis (EDS) to study the development of suicide morphology in response to rapid thermal annealing (RTA). Two sets of specimens have been studied: (i) 32nm Ti thin films on undoped single-crystal Si substrates [Ti/Si] and (ii) 32nm Ti films separated from an undoped single-crystal Si substrate by a 0.12nm thick Mo interlayer [Ti/Mo/Si]. This paper shows structures formed after RTA at a ramp rate 3 °C/sec to 750 °C with a hold of 1 sec

In situ processing of TiN/Si3N4 composites by Ti-Si3N4 solid state reaction

Using an in situ synthesis method, TiN-Si 3 N 4 composites were successfully fabricated by heating mixed powder compacts of Ti and Si 3 N 4 in a nitrogen atmosphere. Mechanical properties with different Ti additions were tested. According to XRD analysis, the TiN and TiSi phases were formed during sintering. No other titanium suicides were found. The microstructure of this materials were investigated by SEM and EDS.

XRD-Studies of SiC/Si layers on carbon substrates

Structural investigations of thin films of SiC, SiC with free silicon and various titanium suicides (TiSi2, TiSi and Ti5Si3) are described. The crystal phases have been identified using X-ray diffractometry. The growth of reaction products from surface reactions between silicon and deposited titanium can be observed.

Laser-Assisted TiSi2 Formation for ULSI Applications

ABSTRACTIn this paper, we describe the results of recent work in which TiSi2 formation on deep-submicron polysilicon gates is achieved using pulsed excimer laser irradiation. Formation of low resistivity titanium suicide on sub-0.1 μm polysilicon lines is confirmed by sheet resistance measurements. High-resolution TEM examination shows exceptionally smooth interface between suicide and heavily-doped silicon substrate. Gate to source/drain bridging is not observed. Analytical techniques including Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD) have been used to characterize the irradiated films. This laser-assisted suicide formation process is a promising technology for extreme submicron MOSFET applications.

STM Study of Initial Growth of Titanium Silicide on Si(III)

ABSTRACTThe nucleation and initial growth of titanium suicide on Si(111)7×7 surface has been studied using the scanning tunneling microscopy(STM) in ultrahigh vacuum. At room temperature Ti atoms react with Si atoms and preferentially adsorb on faulted half of the 7×7 surface. By annealing at 600°C, islandlike structures(amorphous titanium suicide) and striplike structures(crystalline titanium suicide) are formed. Annealing at 700°C drives the growth of striplike structures from islandlike structures. The striplike structures grow parallel to specific directions on the 7×7 surface.

Kinetic analysis of the combustion synthesis of molybdenum and titanium silicides

The temperature profiles associated with the passage of self-propagating combustion waves during the synthesis of MoSi2 and Ti5Si3 were determined. From these profiles, kinetic analyses of the combustion synthesis process for these two silicides were made. The synthesis is associated with high heating rates: 1.3 × 104 and 4.9 × 104 K·s−1 for MoSi2 and Ti5Si3, respectively. The width of the combustion zone was determined as 1.3 and 1.8 mm for the silicides of Mo and Ti, respectively. The degree of conversion, η, and its spatial distribution and the conversion rate, ∂η/∂t, were determined. However, because of the inherent characteristics of wave propagation in MoSi2, only in the case of Ti5Si3 could the activation energy be calculated. An average value of 190 kJ µ mol−1 was determined for titanium suicide.

Observation of Crystallization, Precipitation, and Phase Transformation Phenomena in Si Rich Titanium Silicide Thin Films

ABSTRACTCrystallization, precipitation, and phase transformation phenomena were observed in titanium suicide thin film samples during in situ heating experiments in a transmission electron microscope. The as-deposited TixSiy films were 110 nm in thickness with a composition of 1 Ti to 2.33 Si. Crystallization of the C49 phase was followed isothermally near the sputter deposition temperature. The movement of individual grain boundaries was recorded so that a “velocity of crystallization” could be calculated. The precipitation of excess silicon from the C49 phase was first observed in the 650°C to 750°C temperature range. The precipitates were predominantly of the incoherent type, with a smaller number existing at the grain boundaries. Ostwald ripening then occurred up to the C49 to C54 phase transformation which was accompanied by a dramatic increase in grain size. Grain boundary movement during the phase transformation was such that large precipitates, which were originally at C49-C49 boundaries, ended up within resulting C54 crystals. Many of these larger precipitates were found to exist as epitaxial “islands” at the TiSi2/Si substrate interface.

Reaction layer characterization of the braze joint of silicon nitride to stainless steel

This investigation studies the role of titanium in the development of the reaction layer in braze joining silicon nitride to stainless steel using titanium-active copper-silver filler metals. This reaction layer formed as a result of titanium diffusing to the filler metal/silicon nitride interface and reacting with the silicon nitride to form the intermetallics, titanium nitride (TiN) and titanium suicide (Ti5Si3). This reaction layer, as recognized in the literature, allows wetting of the ceramic substrate by the molten filler metal. The reaction layer thickness increases with temperature and time. Its growth rate obeys the parabolic relationship. Activation energies of 220.1 and 210.9 kj/mol were calculated for growth of the reaction layer for the two filler metals used. These values are close to the activation energy of nitrogen in TiN (217.6 kj/mol). Two filler metals were used in this study, Ticusil (68.8 wt% Ag, 26.7 wt% Cu, 4.5 wt% Ti) and CB4 (70.5 wt% Ag, 26.5 wt% Cu, 3.0 wt% Ti). The joints were processed in vacuum at temperatures of 840 to 900 °C at various times. Bonding strength is affected by reaction layer thickness in the absence of Ti-Cu intermetallics in the filler metal matrix.

Resistivity in weakly disordered suicides induced by ion implantation

The temperature coefficient of electrical resistivity (TCR) of ion implanted suicide films are measured by van der Pauw method. The TCR tends to become small and even changes sign at certain temperatures as the implanted ion energy increases. The experimental data are much pertinent to the theoretical fitting with weak localization at temperature below 90K. However at 90K < T < 160K, the experiment is prevailed by electron phonon interaction in the presence of disorder. The retention of positive TCR of the ion-implanted titanium suicide at a rather high residual resistivity implies an enhancement of the localization effect due to the screening of the electron-phonon interaction by the d-state hybridization of the transition metals.

Ambient and High Temperature STM Investigations of the Growth of Titanium Suicide on Silicon Substrates

A variable temperature scanning tunnelling microscope (STM) in UHV has been used to investigate the growth, morphology and surface atomic structure of ultrathin titanium suicide films on Si(100) and Si(111) substrates. Three stages of suicide growth have been identified based on microstructural considerations. They occur over similar temperature ranges for both substrates and may be summarised as: agglomeration and the formation of disordered islands, crystallite formation, and crystallite growth. Additionally, island burial is found for Si(100) substrates (950°C), and preferential crystallite growth is observed for high temperature processing (1200°C) of titanium silicide on Si(111). Methods for STM crystallography have been developed and used to identify possible epitaxial silicide/silicon relationships based on morphological considerations. Atomic resolution images of titanium silicide crystallites have identified a 2×2 silicon termination of a C54-TiSi2(111) surface, a 2×2 silicon terminated C54-TiSi2(010) surface, and a reconstructed C54-TiSi2(311) surface. It has been concluded that unambiguous identification of epitaxial relationships requires images of the atomic structure of the silicide crystallite surfaces in addition to morphological information.

Evaluation of anomalies during nickel and titanium suicide formation using the effective heat of formation model

The effective heat of formation model allows heats of formation to be calculated as a function of the concentration of the reactants at the growth interface. The effective concentration is taken to be the concentration of the liquidus minimum for the relevant binary system. Using this model, the anomalous and contradictory results for initial formation of titanium silicide phases are ascribed to the two eutectics at 14 and 84 at.% silicon (both at 1330 °C) for the Ti-Si binary system. The native oxide layer usually present on silicon surfaces and the affinity of Ti for oxygen further affect the effective concentration, thereby adding to the contradictory experimental results that have been found. In the Ni-Si system our measurements show that a sufficiently high concentration of oxygen in amorphous silicon can lead to formation of NiSi instead of Ni 2Si, which is normally the first phase to form. This observation, as well as the formation of NiSi 2 as the first phase in the presence of diffusion barriers, is also explained in terms of the effective heat of formation model.

TiSi2 Integrity within a Doped Silicide Process Step

ABSTRACTDegradation of arsenic implanted titanium suicide (TiSi2) thin films as a result of thermal processing for shallow junction formation is investigated. Significant arsenic diffusion from the suicide overlayer into the silicon substrate has been detected by Rutherford Backscattering Spectrometry at drive-in temperatures &gt; 1050°C. Cross-sectional transmission electron micrographs have shown the suicide film become increasingly non-uniform as the thermal budget increases, ultimately leading to discontinuities forming in the suicide film. This observed degradation of the titanium suicide film is also supported by sheet resistance measurements which show the film to degrade significantly above a threshold thermal budget

Synthesis of Ti2N-TiSi2 Layers by One-Step Excimer Laser Irradiation

ABSTRACTIn the present work a novel approach to suicide and nitride formation on the surface of silicon single crystals wafers is reported. The compound growth occurs directly in the place of interest as a result of a laser promoted chemical reaction. Results indicate that it is possible to obtain a titanium nitride layer superimposed on a titanium suicide film with a single-step laser irradiation process. The thickness of the suicide and nitride layers can be adjusted by a proper choice of the laser fluence and number of subsequent pulses.

Comparison of the Interface and Surface Morphologies of Zirconium and Titanium Silicides on Silicon

ABSTRACTThe morphology of zirconium suicide grown on Si(111) is investigated and compared to that of titanium suicide on Si(111) and (100). Zirconium was deposited on atomically clean silicon in UHV, and the suicide was formed by postdeposition annealing. ZrSi2 films formed from ≤100 Å of Zr deposited on Si(111) remained continuous for anneals of 400°C to 700°C. A film formed from 50 Å of Zr on Si(111) remained continuous for anneals up to 800°C, at which point the reappearance of a partial 7×7 LEED pattern indicated island formation. The interfaces of the films, studied by TME, show roughening after suicide formation. These results are compared and contrasted with the islanding behavior of titanium suicides, and analyzed in terms of a liquid-liquid model previously used with TiSi2.

Nucleation and Morphology of TiSi2 on Si

ABSTRACTThis study explores the nucleation and surface and interface morphology of TiSi2 films formed on Si (100) and (111) surfaces. Titanium suicide films were formed on atomically clean Si(111) and (100) surfaces by UHV deposition of Ti followed by in situ anneals. The TiSi2 formation process was characterized is itu using AES and LEED, and the interface structure was determined post preparation by HRTEM. The metastable C49 and stable C54 TiSi2 phases have been identified from Raman spectroscopy measurements. The islands were partially recessed into the substrate, and the shape and degree of recession was different for the islands on (111) and (100) substrates. On (111) substrates epitaxial islands were observed which exhibited different interface structures and epitaxial alignments. The contact angles of the islands were measured and the surface and interface energies of the different configurations were deduced. The mechanisms pertaining to island formation and interface morphology are described in terms of the wetting properties of a liquid-liquid system, with the effects of interface structures causing deviations from the model.

Crystallite Dimensions and Strain in Poly-Si and Ti-Silicide Thin Films Measured with Grazing Incidence X-Ray Diffraction

ABSTRACTThe present study describes the measurement of microcrystalline grain dimensions and crystallite strain for polycrystalline silicon (poly-Si) and titanium suicide, using grazing incidence X-ray diffraction (GIXRD). A variety of poly-Si sample configurations were synthesized by different low pressure chemical vapor deposition (LPCVD) processing techniques. Selected samples were subsequently processed by phosphorous diffusion doping and reaction with thin titanium layers. Characterization with GIXRD reveals differing crystallite grain dimensions, ranging from =80Å to =900Å. Crystal strain was measured in direction perpendicular to (111) lattice planes. Phosphorous diffusion doping is shown to remove this (111) strain, in addition to increasing crystallite grain dimensions. The GIXRD characterization, which measures a specific fraction of the sample crystal texture, indicates that deposition rate modulated poly-Si LPCVD reduces (111) microscopic strain in poly-Si films two-fold, compared to conventional poly-Si deposition. The crystallite dimensions of conventional poly-Si, are found to peak approximately in direction perpendicular to (110) planes. The same trend is observable for deposition rate modulated poly-Si, where grain dimensions, measured in [110] direction, are reduced by =30%. Larger crystallite dimensions were measured in direction perpendicular to (110) planes, for both cubic poly-Si and orthorhombic Ti-silicide layers, suggesting the presence of preferred crystallite growth directions, resulting in anisotropie crystallite grain dimensions.

Matrix/reinforcement interactions in shock-wave consolidated titanium aluminide reinforced with SiC

Explosive shock-wave consolidation has been used to fabricate a composite consisting of gamma phase titanium aluminide matrix reinforced with paniculate silicon carbide. Although the consolidation process takes less than a microsecond to complete, melting of the surfaces of the titanium aluminide powder particles results in a reaction with the silicon carbide. Titanium suicide and titanium carbide form in the molten zone, depleting it of titanium to the extent that its final composition is TiAl3. In addition, a second titanium suicide phase forms on the surfaces of the silicon carbide particles.

Characterization of a rapid thermal anneal TiNxOy/TiSi2 contact barrier

In this paper, the physical and electrical properties of a TiNxOy/TiSi2 dual layer contact barrier are reported. The TiNxOy/TiSi2 barrier was formed by rapidly annealing a Ti thin film on Si in an N2 ambient. During this process, the Ti film surface reacts with N2 to form a TiNxOy skin layer and the bulk of the Ti film reacts with Si to form an underlying TiSi2 layer. The influences of rapid thermal anneal (RTA) conditions on the TiNxOy layer were investigated by varying the RTA temperature from 600 to 1100° C and cycle duration from 30 to 100 s. It is found that the resulting TiNxOy and TiSi2 layer thicknesses are dependent on RTA temperature and the starting Ti thickness. For a starting Ti thickness of 500A, 150A thick TiNxOy and 800A thick TiSi2 are obtained after an RTA at 900° C for 30 s. The TiNxOy thickness is limited by a fast diffusion of Si into Ti to form TiSi2. When a Ti film is deposited on SiO2, Ti starts to react with SiO2 from 600° C and a significant reduction of the SiO2 thickness is observed after an RTA at 900° C. The resulting layer is composed of a surface TiNxOy layer followed by a complex layer of titanium oxide and titanium suicide. In addition, when Ti is depos-ited on TiSi2, thicker TiNxOy and TiSi2 layers are obtained after RTA. This is because the TiSi2 layer retards the diffusion of Si from the underlying substrate into the Ti layer. NMOSFETs were fabricated using the TiNxOy/TiSi2 as a contact barrier formed by RTA at 900° C for 30 s and a significant reduction of contact resistance was obtained. In addition, electromigration test at a high current density indicated that a significant improvement in mean time to failure (MTF) has been obtained with the barrier.

Pulsed laser synthesis of titanium silicides using a Q-Switched Nd: Glass laser

Titanium films 120 nm thick deposited on single-crystalline silicon (c-Si) as well as poly-Si/SiO2/c-Si substrates were subjected to Nd: glass laser irradiation. Laser fluences of 1,1.5, and 2 J/cm2 were used at the pulse duration of 30 ns. From RBS analysis it follows that on c-Si substrate titanium suicide is formed using one pulse of 1.5 J/cm2 energy density. On the substrate with surface overlayers lower fluence (1 J/cm2) was sufficient. Under these conditions the sheet resistance of the samples decreased from the initial value 5 Ω/□ to 2–3 Ω/□. The smaller threshold density of energy for suicide formation in Ti/polySi/SiO2/c-Si structure is shown to be a consequence of the SiO2 underlayer, which is a poorer heat conductor than silicon. The experimental results of the suicide synthesis are in semi-quantitative accordance with the numerical computations of the temperature vs time evolution and depth temperature distribution in our samples.

Structural Transitions in Titanium/Amorphous-Silicon Multilayers

We report a quantitative investigation of silicidation in Ti/amorphous-Si thin-films using Differential Scanning Calorimetry (DSC), thin-film X-ray diffraction and Cross-sectional Transmission Electron Microscopy (XTEM). Multilayered thin films were used to facilitate calorimetric observation of the heat released or absorbed at many reacting interfaces. It is shown that calorimetric analysis, combined with structural analysis using X-ray diffraction and XTEM, is effective in providing both kinetic and thermodynamic information about interdiffusion reactions in thin films. The present paper describes experimental results for multilayers with an atomic concentration ratio of 1 Ti to 2 Si and modulation periods ranging from 10 to 60 nm. A thin amorphous titanium suicide layer was found to exist between the as-deposited Ti and a-Si layers. Heating the multilayer film caused the amorphous Ti-silicide to grow over a broad temperature range by an exothermic reaction. An endothermic relaxation occurs during the late stage of amorphous suicide growth. Heating to temperatures over 800K causes C49-TiSi2 to form at the a-si1icide/a-Si interface. Temperatures at which all the above structural transitions occur vary with modulation period. Analysis of the DSC data indicates an activation energy of 3.1 eV for the formation of C49-TiSio, which is attributed to both the nucleation and the early growth of the suicide. The heat of formation for C49-TiSi2 from a reaction of a-silicide and a-Si was found to be -30±5KJ/mol. Nucleation appears to be the controlling step in C49-TiSi2 formation.